Thermal balance temperature control system

ABSTRACT

A method and apparatus for controlling a temperature-regulated zone utilizing a thermal balance temperature control system. The thermal balance control system is a dynamic real time control system that measures the sensible thermal load in the zone, and directly regulates the BTU output of the HVAC package to balance such output with the measured sensible thermal load.

This application claims the benefit of U.S. Provision Application Ser.No. 60/512,410 filed on Oct. 17, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to a temperature control system and, moreparticularly, to a system which directly regulates the system output tobalance such output with the sensible thermal load.

Heating, ventilating and air-conditioning (HVAC) systems are used toboth heat and cool the air within an enclosure, e.g., a building or zonewithin such building. An HVAC system typically includes a heating unit,a cooling unit, a supply air fan, a supply duct for directing air intothe enclosure, and a return duct for removing air from the enclosure. Itwill be appreciated by those skilled in the art that HVAC systems aregenerally designed to operate in one of three modes: a heating mode toheat the enclosure, a cooling mode to cool the enclosure and aeconomizer mode to ventilate the enclosure. The economizer modetypically utilizes both an outdoor air damper and a return air damper,commonly referred to as an economizer, that can be selectively modulatedopened to allow the return air to mix with fresh outside air.

There is typically a control system associated with an HVAC system, suchcontrol system including a thermostat (typically located within theenclosure) and associated hardware/software for controlling thecomponents of the particular HVAC system in response to pre-programmedinstructions. Typically, the control system allows a user to pre-selectone of the three operating modes, as well as selecting a desiredtemperature for the enclosure. Thereafter, the control system activateseither the heating or cooling portion of the HVAC system to maintain thepre-selected temperature within the enclosure. Under certain conditionsthe economizer mode may be able to maintain the enclosure at thepre-selected temperature.

When set in the cooling mode, the control system will provide cold airto the enclosure when the temperature of the enclosure exceeds thepre-selected temperature. The control system accomplishes this task byactivating the cooling unit (or stage of a multi-stage cooling unit) andthe supply air fan. The supply air fan blows the air through the coolingunit and into the enclosure. As a result of the cold air entering theenclosure, the temperature in the enclosure is lowered. Once thetemperature in the enclosure falls below the pre-selected temperature,the thermostat in the enclosure provides a signal to the control systemwhich either turns off the cooling unit, or turns off a stage of cooling(if part of a multi-stage unit).

Similarly, when set in the heating mode, the control system will providehot air to the enclosure when the temperature of the enclosure fallsbelow the pre-selected temperature. The control system accomplishes thistask by activating the heating unit (or stage of a multi-stage heatingunit) and the supply air fan. The supply air fan blows the air throughthe heating unit into the enclosure. As a result of the hot air enteringthe enclosure, the temperature in the enclosure is raised. Once thetemperature in the enclosure rises above the pre-selected temperature,the thermostat in the enclosure provides a signal to the control unitwhich either turns off the heating unit, or turns off a stage of heating(as part of the multi-stage unit).

As mentioned, the economizer mode may be able to maintain the enclosureat the pre-selected temperature under certain conditions. Particularly,during times when the outside air temperature is low (e.g., 50° F.), andthe control system needs to provide cold air to the enclosure to coolsuch enclosure, the system can utilize the economizer mode to providethe desired cold air to the enclosure. In the economizer mode, thecontrol system will selectively modulate open and close both an outsideair damper and a return air damper to mix the cool outside air with thewarmer return air. In this manner, the air being supplied to theenclosure is cooled to the desired temperature without the need foractivating the cooling unit. Of course, if the outside air temperatureis too high and/or too humid, the cooling unit will need to beactivated.

The above-described temperature control systems are typically designedto allow “time cycling” of the heating/cooling components, which ofcourse limit/preclude these known systems from regulating the BTU outputof the HVAC to balance such output with the measured sensible thermalload.

More to the point, those skilled in the art will appreciate that “timecycling” prevents a system from operating in a “real time” mode, andoften allows undesirable temperature swings, as well as inefficientoperation of the individual components. This inefficient operation caninclude the operation of excess cooling/heating capacity (resulting inunneeded energy costs) and excess cycling of the systems components(resulting in the shortening of the life of the unit and/or an increasein maintenance of such unit). In fact, the prior art has generallybelieved that real time temperature control systems which attempt todirectly regulate BTU output to balance such output with the system loadare inherently unstable, and will produce excessive and potentiallydamaging “short cycling” of the heating/cooling components.

Moreover, the prior art systems are generally inefficient because thesupply air is often colder/hotter than necessary to satisfy the measuredsensible thermal load. Finally, such systems are generally incapable ofsatisfying an unmet cooling/heating load.

There is therefore a need in the art for a dynamic real time temperaturecontrol system which directly regulates the BTU output of an HVACpackage to balance such output with the sensible thermal load beingmeasured in the temperature-regulated enclosure, therebyeliminating/reducing undesirable temperature swings in the regulatedenvironment, reducing excess cycling of components andeliminating/reducing utilization of unneeded excess capacity.

SUMMARY OF THE INVENTION

The present invention, which addresses the needs of the prior art,relates to a method of controlling room temperature within a zone of atemperature control system. The method generally includes the steps ofdefining a thermal demand set point temperature curve for thetemperature control system, measuring a sensible thermal load within thezone, calculating a thermal demand set point temperature based upon thesensible thermal load, defining at least one load band for thetemperature control system corresponding to an equilibrium condition,and operating the temperature control system to maintain individualcomponents of the system in a constant operating condition for as longas the system operates within the load band.

The present invention further relates to a thermal balance temperaturecontrol system for controlling room temperature within a predefinedzone. The system includes at least one air handling unit for providingsupply air at a preselected temperature, the air handling unit includesat least one unit stage. The system further includes a supply duct fortransporting supply air from the air handling unit to the predefinedzone. Finally, the system includes at least one controller forcontrolling room temperature within the predefined zone. The controllercomprises at least one processor circuit for measuring a sensiblethermal load within the zone and for calculating a thermal demand setpoint temperature based upon the sensible thermal load in accordancewith a predefined thermal demand set point temperature curve. Theprocessor circuit operates the temperature control system to maintainthe unit stage in an energized condition for as long as the systemoperates within a predefined load band corresponding to an equilibriumcondition.

Finally, the present invention relates to a controller for controllingroom temperature within a zone of a temperature control system. Thecontroller includes at least one processor circuit for measuring asensible thermal load within the zone and for calculating a thermaldemand set point temperature based upon the sensible thermal load inaccordance with a predefined thermal demand set point temperature curve.The processor circuit operates the temperature control system tomaintain individual system components in a constant operating conditionfor as long as the system operates within a predefined load bandcorresponding to an equilibrium condition.

As a result, the present invention provides a dynamic real timetemperature control system which directly regulates the BTU output of anHVAC package to balance such output with the sensible thermal load beingmeasured in a temperature-regulated enclosure, therebyeliminating/reducing undesirable temperature swings in the regulatedenvironment, reducing excess cycling of components andeliminating/reducing utilization of unneeded excess capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematical representation of a heating, ventilating and airconditioning system including the thermal balance temperature controlsystem of the present invention;

FIG. 2 is a schematical representation of the components of an HVACpackage used in accordance with the present invention;

FIG. 3 is a graphical representation of the thermal demand set pointtemperature curve for the thermal balance temperature control system ofthe present invention;

FIG. 4 is a graphical representation of a cooling load band curve forthe thermal balance temperature control system of the present invention;

FIG. 5 is a graphical representation of an economizer load band curvesuperimposed on the curve of FIG. 4; and

FIG. 6 is a schematical representation of the controller used inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As discussed more fully hereinbelow, the present invention is directedto a method and apparatus for controlling a temperature-regulated zoneutilizing a thermal balance temperature control system. The thermalbalance control system is a dynamic real time control system thatconstantly measures the sensible thermal load in the mentioned zone, anddirectly regulates the BTU output of the HVAC package to balance suchoutput with the measured sensible thermal load, thus providing a stateof system equilibrium. The system will continue to operate in thisequilibrium state (without time cycling of any heating/coolingcomponents) until the system measures a change in the sensible thermalload within the mentioned zone.

The sensible thermal load is the amount of deviation (measured indegrees) between the set point temperature for the zone and the actualzone temperature. When the actual room temperature is above the setpoint temperature, the sensible thermal load is a cooling load, and thesystem must therefore reduce the supply air temperature to balance theBTU output of the HVAC package with such load. If the actual roomtemperature is below the set point temperature, then the sensiblethermal load is a heating load, and it is necessary for the system toincrease the supply air temperature to balance the BTU output with suchload.

The thermal balance control system of the present invention utilizes theformula: Thermal Transfer Rate (BTU/HR)=Supply Air Volume (cubic feetper minute)×1.08×(Room Temperature-Supply Air Temperature). As will beappreciated from the foregoing formula, the thermal transfer rate isequal to 0 when the room temperature is equal to the supply airtemperature.

As discussed herein, the thermal balance control system of the presentinvention operates in a “load cycling” manner, in contrast to the “timecycling” manner of conventional units. It will be appreciated thatavailable HVAC units which operate in an on/off function (e.g., directexpansion (DX) cooling, electric heat, etc.) are typically utilized in atime-cycled manner. Particularly, if the prior art system requiressupply air at 55° and stage 1 of a DX cooling system only reduces thetemperature to 60°, the second stage of such system will be cycled onand off to reduce the temperature of the supply air to below 55°. Everytime a unit cycles on and off the system can experience wide andcomfortable temperature swings. With respect to the cycling on and offof a DX cooling unit, condensation caught in a coil will evaporate backinto the supply air when such unit is cycled off. This increase inhumidity of the supply air can cause discomfort to the occupants in thebuilding, and also decreases the overall efficiency of the unit (in thatthe unit must again remove the vapor from the air when cycled back on).For example, the cycling of a stage of DX cooling on a rainy summer daymay cause such an undesirable condition.

Referring to FIG. 1, a thermal balance temperature control system 10 inaccordance with the present invention includes a heating, ventilatingand air conditioning (HVAC) package 12 for supplying cold or heatedsupply air 14 (as well as fresh outside air) into a supply air duct 16,which communicates with an interior enclosure, i.e., zone 18. Return air20 is thereafter removed from zone 18 via return air duct 22.Temperature control system 10 also includes a thermal balance controller24, which is a dynamic real time controller that measures the sensiblethermal load in zone 18, and regulates the output capacity of HVACpackage 12 to balance such output with this measured load.

As shown in FIG. 2, HVAC package 12 includes a supply air fan 26 formoving supply air into zone 18 and a return air fan 28 for removingreturn air from zone 18. HVAC package 12 further includes an economizersection 30, a heating unit 32, a cooling unit 34 and a supply airtemperature sensor 36. Package 12 may also include a filter 38, a lowtemperature alarm 40 and low limit temperature sensor 42.

Economizer section 30 preferably includes an exhaust damper 44, anoutside air damper 46 and a return air damper 48. Return air damper 48,together with outside air damper 46, control the percent mixture ofreturn air/fresh air being fed into supply air duct 16. Those skilled inthe art will understand that exhaust damper 44, outside air damper 46and return air damper 48 are preferably operated to meet at least someof the following goals: 1) to operate in economizer mode when conditionspermit; 2) to take maximum advantage of the temperature of the returnair; and 3) to mix sufficient fresh air into the supply air.

In one preferred embodiment, HVAC package 12 includes an economizersection, a two-stage gas heating section, a three-stage direct expansion(DX) cooling unit, a constant volume supply fan and a constant volumereturn air fan. One preferred package is rated at 25 tons at 10,000cubic feet per minute. This design capacity is based on approximately400 cubic feet per minute per ton, and 5-6 air changes per hour. Theoperation sequence of HVAC package 12 preferably follows an ASHRAE CycleII.

Thermal balance temperature control system 10 can be used in a constantvolume system or in a variable air volume (VAV) system. It will berecognized by those skilled in the art that a VAV system would utilizevariable speed supply and return fans (in contrast to the constant speedfans used in a constant volume system). Unlike the constant volumesystem, the VAV system will typically include a differential pressuregauge located in the supply air duct downstream from the supply air fan.

Thermal balance temperature control system 10 may operate in either theheating, economizer or cooling mode, depending on the sensible thermalload measured within zone 18. More particularly, the heating mode ispreferably controlled by cycling (in sequence) the two gas valves tomaintain a desired supply air temperature. The heating mode is generallynot initiated until outside air damper 46 is at its minimum opensetting. Preferably, morning warm-up will be accomplished with bothoutside air damper 46 and exhaust damper 44 fully closed, and returndamper 48 fully opened. The economizer cooling mode is preferablycontrolled by modulating exhaust damper 44, outside air damper 46 andreturn air damper 48 to maintain the desired supply air temperature. Theeconomizer cooling mode is preferably limited by an outside airtemperature sensor set at 60° that reduces the intake of fresh outsideair (for ventilation) to a minimum value at temperatures exceeding 60°.Of course, this 60° setting is adjustable, depending on system criteria.Finally, the cooling mode is preferably controlled by cycling the stagesof cooling in direct relation to the sensible thermal load measuredwithin zone 18. Because temperature control system 10 seeks to balancethe BTU output of HVAC package 12 with the sensible thermal loadmeasured within zone 18, the stages of heating and cooling do notexperience short cycling (i.e., excessive cycling on and cycling off ofthe individual stages). Rather, such stages remain activated until suchtime as the system measures a change in the sensible thermal load.

It will be appreciated by those skilled in the art that a multi-stageheating/cooling unit generally provides better overall efficiency. Forexample, in a multi-stage cooling unit having three stages, each stageproviding approximately 33% of the total cooling capacity of the unit.When maximum cooling is required, all three stages can be activated.However, when maximum system output is not needed, one or more stagescan be deactivated, thus allowing the system to operate in a moreenergy-efficient mode. Similarly, each stage in a two-stage unitprovides 50% of the total capacity of the unit, while each stage of afour-stage unit provides 25% of the total capacity. In one embodiment,the relay differential of a stage of cooling is made greater then thetemperature change which results from that stage being energized ordeenergized. This prevents the cooling stage from short cycling due tothe action of the discharge sensor. Preferably, the relays should be setup to provide Vernier controls.

It will be understood by those skilled in the art that resetting thetemperature of the supply air in response to certain system measurementscan improve the performance and operation of the overall system.Although prior art systems utilize reset schedules, such schedulesgenerally consist of a standard fixed ratio which does not directlycorrelate to the operating characteristics of the system and does notallow the system to reach a state of equilibrium. In contrast, thethermal demand set point temperature curve for the system of the presentinvention (as shown in FIG. 3) is established to directly correlate withthe operating characteristics of HVAC package 12 and to allow the systemto reach a state of equilibrium (i.e., the BTU output is balanced withthe measured sensible thermal load).

Referring now to FIG. 3, the illustrated thermal demand set pointtemperature curve for HVAC package 12 includes a heating portion and acooling portion. For example, if the particular heating unit is capableof providing a maximum temperature rise of 50°, then the heating portionof the curve is drawn to extend between a minimum thermal demand setpoint P₀ (wherein 0 heat is required) and a maximum thermal demand setpoint P₁ (wherein maximum heat, i.e., plus 50° F.) is required. Thismaximum heat condition corresponds to a measured sensible thermal loadof −2° F. The cooling portion of the curve is drawn in accordance withthe particular cooling unit installed in the system. For example, if thesystem is capable of reducing the supply air temperature by a maximum of25°, then the curve is drawn between a minimum thermal demand set pointP₀ (wherein 0 cooling is required) and a maximum thermal demand setpoint P₂ (wherein maximum cooling, i.e., minus 25° F.,) is required.This maximum cooling condition corresponds to a measured sensiblethermal load of +2° F.

The thermal demand set point temperature curve of FIG. 3 is based upon atemperature band of plus and minus 2° F. On a drop in space temperatureof 2° F., the supply air temperature will be reset from set pointtemperature P₀ to P₀ plus 50° F. On a rise in space temperature of 2°F., the supply air temperature will be reset from set point temperatureP₀ to P₀ minus 25° F. This band can, of course, be widened (althoughwidening the band may cause the temperature in zone 18 to move into anuncomfortable region), may be narrowed (which may increase the cost ofoperating such system) or may include integral control action forimproved responsiveness.

The method of the current system will now be described with respect toFIGS. 3 and 4. As described, FIG. 3 is used to calculate the thermaldemand set point temperature of the supply air during operation of thesystem. To begin, the sensible thermal load in zone 18 is measured. If,for example, the room set point is 73° F. and the actual measured roomtemperature is 74° F., the deviation from set point (i.e., the sensiblethermal load) is +1°. Referring to the thermal demand set pointtemperature curve of FIG. 3, a +1 temperature deviation is within thecooling portion of the curve and corresponds to approximately −12.5° onthe Y axis. The set point P₀ of FIG. 3 corresponds to the set pointtemperature of zone 18. Thus, the thermal demand set point temperaturefor the supply air would be calculated to be 73°−12.5°=60.5°. This isthe temperature at which the system is balanced, i.e., providing supplyair at 60.5° F. to zone 18 will maintain zone 18 in a state ofequilibrium at 74° F.

In certain applications, as described in commonly-owned co-pending U.S.application Ser. No. 10/704,251 filed Nov. 7, 2003, the disclosure ofwhich is incorporated herein by reference, the system can be designed torecognize this unmet cooling load (i.e., the +1° F. in zone 18).Thereafter, the system would calculate and supply the additional coolingnecessary to move the actual room temperature towards the room setpoint.

FIG. 4 illustrates the novel load band curve of the present invention,which is preferably a proportional curve having preselected parameterswhich correspond to the components of the system. The particular graphshown in FIG. 4 represents a plot for a multi-stage DX cooling systemhaving three stages wherein the maximum cooling is approximately 20°. A40% allowance (i.e., 8°) may be designed into the system such that the Xaxis extends from 0° to 28° (20°+(40% of 20°)). The X axis of the loadband is 10° wide (i.e., it extends from 9° to 19°). It will beappreciated that each stage of the three stage DX cooling system iscapable of approximately a 7° temperature drop. Again, a 40% allowancemay be designed into the system to provide a total of approximately 10°(7°+(40% of 7)=9.8, which is approximately 10°).

If the desired supply air temperature is calculated to be 60.5° (asdiscussed hereinabove), the set point S of the graph of FIG. 4 will beset to 60.5°. The value of this point will remain fixed until the systemmeasures a change in the sensible thermal load in zone 18 andrecalculates the thermal demand set point temperature from FIG. 3. Theactual supply air temperature (as measured by sensor 36) is then plottedalong the curve. With set point S set at 60.50° F., point S₁ willcorrespond to 55.5° F. and point S₂ will correspond to 65.5° F.

The first stage of cooling will be turned on, resulting in a 7° drop oftemperature. If this is sufficient to bring the supply air temperaturewithin the load band which, in this example, will extend from 55.5° to65.5° (5° on either side of the set point), then no additional stageswill be turned on. As long as the supply air temperature remains withinthis load band, the first stage of the compressor will remain on. Unlikeconventional systems which would automatically begin time cycling thisstage of the compressor, the system of the present invention will allowthis stage of the compressor to stay on as long as the supply airtemperature remains within in such load band. In other words, thethermal balance control of the present invention has reached a state ofsystem equilibrium, and may remain in this state until a change in thesensible thermal load is measured.

The portion of the curve of FIG. 4 extending from point S₁ to S₂ isreferred to herein as the load band. Once the supply air temperaturemoves outside of the load band, it moves into one of two integratingregions. For example, if two stages of the three stage compressor are onand the supply air temperature continues to decrease such that it movesdown the curve into the lower integral region, an integral factor willincrease the speed at which the supply air temperature moves towards thestage-off point. Once, the supply air temperature hits this point, theparticular stage is turned off, thereby raising the supply airtemperature and pushing such supply air temperature back towards theload band. Likewise, if the supply air temperature increases such thatit moves up the curve into the upper integral region, eventuallyadditional stages of cooling will be turned on. Again, integral actiondecreases the time necessary to reach the point where an additionalstage of cooling is turned on. Thus, the system anticipates overcoolingand undercooling through the integral action portions of the controlsystem.

More particularly, the system anticipates a change in the sensiblethermal load. If the load is increasing (thus indicating the need for anextra stage of cooling), the thermal demand set point temperature willdecrease (thus providing a lower set point to the cooling controlmodule). The supply air temperature will now be higher than the thermaldemand set point temperature, and will begin to move up the curve intothe upper integral region. An integral factor will increase the speed atwhich the supply air temperature moves towards the stage-on point. Ifthe sensible thermal load is decreasing, the reverse action will occur.As a result, the system provides load change anticipation.

Stated differently, the present invention anticipates gain in the wrongdirection, and corrects this unwanted gain prior to the regulatedenclosure experiencing an uncomfortable temperature swing. It will beappreciated by those skilled in the art that although a conventionalsystem would eventually compensate for the change in the temperature ofthe supply air, because of the inherent time delays and time constantsassociated with HVAC systems, the conventional system cannot responduntil “after the fact”. In other words, the regulated enclosure hasalready undergone the unwanted temperature swing before it begins toreact to the temperature swing due the change in the temperature of thesupply air.

FIG. 5 illustrates an economizer load band curve superimposed on thecooling load band curve of FIG. 4. In this particular example theeconomizer load band will extend plus and minus 1.5° from set point S.Once the supply air temperature has increased 1.5° above set point S,the system will begin to modulate open the outside air damper.Similarly, once the supply air temperature decreases 1.5° below setpoint S, the system will begin to modulate closed the outside airdamper. While the supply air temperature is within the economizer loadband, the outside air damper will be maintained in a constant position.

Referring to FIG. 6, the control system of the present invention, i.e.,controller 24, uses three individual control modules, namely a firstcontrol module 50 for the heating unit, a second control module 52 forthe economizer unit and a third control module 54 for the cooling unit.The control system is designed so that each one of the individualcontrol modules operates its respective unit depending on whether thesupply air temperature is above or below the thermal demand set pointtemperature calculated from FIG. 3.

The system calculations and operations described hereinabove arepreferably performed by controller 24, and particularly by theindividual control modules. More particularly, the controller and/orcontrol modules preferably include hardware/software which is capable ofperforming the mentioned calculations, and of utilizing predefinedthermal demand set point temperature and load band curves to control theoperations of system 10 in accordance with the parameters describedherein.

It should be noted that each control module receives two sets ofnumbers. Specifically, each module receives the thermal demand set pointtemperature T_(P) for the supply air (from FIG. 3), and the actualtemperature of the supply air T_(SA) (as measured by sensor 36).Moreover, each control module has a specific temperature set point thatis used to determine which of three individual modules is activated. Thespecific temperature set point for each module is based on the thermaldemand set point temperature, as well as a predefined bias setting.

In a preferred embodiment, the modules are all biased to control at adifferent temperature based on the thermal demand set point temperaturefor the supply air so that only a single module will activate at any onetime. Depending on whether the supply air is above or below each one ofthe module's specific temperature set points determines which unit willbe activated, and thus controlling the system. For example, should theactual supply air temperature (as measured by sensor 36) be below thethermal demand set point temperature, the heating control module wouldbe activated to raise the temperature of the supply air. During thistime, the cooling control module and economizer control module are notactivated since the supply air temperature is below their specifictemperature set points. As mentioned, the heating, economizer andcooling control modules are set up with a predefined bias setting. Theheating control module has a bias setting of −3° F., the economizercontrol module has a bias setting of 0° F., and the cooling controlmodule has a bias setting of +2° F. These bias set point are of courseadjustable.

Referring back to the example set forth above wherein the thermal demandset point temperature for the supply air was calculated to be 60.5° F.,the local set point of the heating control module would be calculated tobe 60.5°−3°=57.5° F. The local set point for the economizer controlmodule would be calculated to be 60.5° F.+0°=60.5° F., while the localset point for the cooling control module would be calculated to be 60.5°F.+2.5° F.=63° F.

The local set point separates the control action of the individualcontrol modules. If the supply air temperature (as measured by sensor36) is below 57.5° F. (the local set point of the heating controlmodule) the system will add heat to satisfy the demand. If the supplyair temperature (as measured by sensor 36) is above 60.5° F. (the localset point of the economizer control module) and cool outside air isavailable the economizer control module will modulate damper 46 satisfythe demand. If the outside air temperature is above a predefinedtemperature limit, the cooling control module will cycle the cooling tosatisfy the demand. Finally, if the supply air temperature (as measuredby sensor 36) is above 63° F. (the local set point of the coolingcontrol module), the system will cool the supply air to satisfy thedemand.

The set point of each control module is 50. Each control module definesa load band and upper and lower integrating regions (for loadanticipation). The heating control module is reverse acting, and theeconomizer and cooling control modules are direct acting.

The control modules are set up to stabilize whenever the supply airtemperature is within the load band. The system then stabilizes at thatlevel of BTU output, i.e., it will stay there until there is a change inthe sensible thermal load in the zone. The load band is set up to matchthe BTU output to the measured sensible thermal load. The loadanticipation feature operates when the sensible thermal load changes,indicating a required increase or decrease in the BTU output of the HVACpackage.

For heating control applications, the heating control module can be setup for single control, multiple-stage control, or modulating control.For economizer control applications, the economizer control module canbe set up for mixing damper control with minimum damper position ormodulating a free cooling valve with a high temperature limit. For DXcooling control applications, the cooling control module can be set upto utilize the load band and load anticipation adjustments to provideload cycling. When a stage of DX cooling is energized the stage willstay ON until there is a decrease in the measure sensible thermal load.The system provides load cycling of the DX stages, not time cycling. Thecontrol module will lengthen the ON time of a stage of cooling if thereis an increase in the latent load on the unit, internal or external.

In accordance with the present invention, control system 10 caneliminate droop, overshoot and mechanical lag by providing the optimumcycle rate of any stage for efficient operation under all loadconditions. Control system 10 can respond immediately to a change in themeasured sensible thermal load by optimizing the cycle rate of theheating or DX cooling stages or repositioning the mixed air dampers.Control system 10 can also respond immediately to the measured change inthe BTU output of the HVAC package (due to changes in the outdoor airtemperatures) by optimizing the cycle rate of the heating or DX coolingstages or repositioning the mixed air dampers.

Control system 10 can dynamically optimizes the cycling rate of theheating or cooling stages based on the BTU output of the HVAC package bymeasuring the supply air temperature and adjusting the cycle rate tomatch the BTU output to the measured sensible thermal load. The cyclerate can be adjusted real time to match the BTU output to the load; thesystem does not compute the cycle rate based on a developed softwareprogram. The load response of control system 10 can be characterized byautomatic initialization of the stages for an optimum cycle rate.

Control system 10 can adapt to the operating characteristics of thevarious modes, heating, economizer and cooling, whether staging orproportional. The control system can match the BTU output of the unit tothe load in the space without cycling from one mode to the other orshort cycle between stages. The control system does not require timedelays between stages. Control system 10 can adapt automatically to achange in the latent load in the space of a change in the temperature ofthe outside ventilation air, and vary the cycle rate of DX cooling foroptimum latent heat removal and improved IAQ.

Control system 10 will not heat and cool simultaneously, nor will itcycle between heating and cooling. Control system 10 does not require aheating or cooling mode switch. Rather, the system can measure the loadand responds accordingly.

Control system 10 can recognize changes in the load, either internal(space) or external (entering the unit) that will affect therelationship of matching the BTU output to the measured sensible thermalload, and can respond immediately.

Control system 10 can identify a stage failure, heating or cooling, andcan activate the next stage if available and activate an alarm. Controlsystem 10 can monitor the HVAC package performance continuously. Anymalfunction can be alarmed, if desired.

It will be appreciated that the present invention has been describedherein with reference to certain preferred or exemplary embodiments. Thepreferred or exemplary embodiments described herein may be modified,changed, added to or deviated from without departing from the intent,spirit and scope of the present invention, and it is intended that allsuch additions, modifications, amendment and/or deviations be includedwithin the scope of the following claims.

1. A method of controlling room temperature within a zone of atemperature control system utilizing supply air having a temperature T,comprising the steps of: defining a thermal demand set point temperaturecurve for said temperature control system; measuring a sensible thermalload within said zone; calculating a thermal demand set pointtemperature based upon said sensible thermal load; defining at least oneload band for said temperature control system corresponding to anequilibrium condition; and operating said temperature control system tomaintain individual components of said system in a constant operatingcondition for as long as said system operates within said load band. 2.The method according to claim 1, wherein said first defining stepincludes the steps of establishing a heating curve extending between aminimum heating thermal demand set point corresponding to a condition ofminimum heating output and a maximum heating thermal demand set pointcorresponding to a condition of maximum heating output and establishinga cooling curve extending between a minimum cooling thermal demand setpoint corresponding to a condition of minimum cooling output and amaximum cooling thermal demand set point corresponding to a condition ofmaximum cooling output.
 3. The method according to claim 2, wherein saidsensible thermal load is equal to the amount of deviation between a setpoint temperature for said zone and an actual room temperature for saidzone, and wherein said measuring step includes the step of calculatingthe difference between said set point temperature and said actual roomtemperature.
 4. The method according to claim 3, wherein saidcalculating step includes the further steps of: establishing a point onsaid thermal demand set point temperature curve corresponding to saidsensible thermal load; determining a delta temperature T from said setpoint temperature; and calculating said thermal demand set pointtemperature based upon said room set point temperature and said deltatemperature T.
 5. The method according to claim 4, wherein said seconddefining step includes the steps of establishing an operating load bandhaving a preselected width corresponding generally to the operatingcharacteristics of a unit temperature control stage.
 6. The methodaccording to claim 5, further comprising the step of defining an upperintegrating region located above said operating load band and a lowerintegrating region located below said operating load band; and providingintegrating action for increasing the responsiveness of said system whena signal enters one of said upper and lower integrating regions.
 7. Themethod according to claim 6, wherein said operating step includes thestep of energizing a temperature control unit stage to move saidtemperature T of said supply air into said load band, and maintainingsaid unit in an energized state as long as said temperature T remainswithin said load band.
 8. A thermal balance temperature control systemfor controlling room temperature within a predefined zone, comprising:at least one air handling unit for providing supply air at a preselectedtemperature, said air handling unit including at least one unit stage; asupply duct for transporting said supply air from said air handling unitto said predefined zone; at least one controller for controlling roomtemperature within said predefined zone, said controller comprising atleast one processor circuit for measuring a sensible thermal load withinsaid zone and for calculating a thermal demand set point temperaturebased upon said sensible thermal load in accordance with a predefinedthermal demand set point temperature curve, and wherein said processorcircuit operates said temperature control system to maintain said unitstage in an energized condition for as long as said system operateswithin a predefined load band corresponding to an equilibrium condition.9. The system according to claim 8, wherein said sensible thermal loadis equal to the deviation between a set point temperature for said zoneand an actual room temperature for said zone.
 10. The system accordingto claim 9, wherein said predefined thermal demand set point temperaturecurve includes a heating curve extending between a minimum thermaldemand set point corresponding to minimum heating output and a maximumthermal demand set point corresponding to maximum heating output andalso includes a cooling curve extending between a minimum thermal demandset point corresponding to minimum cooling output and a maximum thermaldemand set point corresponding to maximum cooling output.
 11. The systemaccording to claim 11, wherein said predefined load band includes anupper integrating region located above said operating load band and alower integrating region located below said operating load band, andwherein said integrating regions provide integrating action forincreased responsiveness to signals entering one of said upper and lowerintegrating regions.
 12. A controller for controlling room temperaturewithin a zone of a temperature control system utilizing supply air A,said supply air having a temperature T, comprising: at least oneprocessor circuit for measuring a sensible thermal load within said zoneand for calculating a thermal demand set point temperature based uponsaid sensible thermal load in accordance with a predefined thermaldemand set point temperature curve, and wherein said processor circuitoperates said temperature control system to maintain individualcomponents in a constant operating condition for as long as said systemoperates within a predefined load band corresponding to an equilibriumcondition.